The invention relates to papermaking machinery and methods. The invention relates more particularly to the manufacture of creped tissue paper.
In the production of tissue for use in personal hygiene products and the like, it is desired to produce a tissue with good tactile qualities (i.e., soft to the touch) while also achieving a high machine speed and efficiency. The speed and efficiency are often limited by the performance of the dry end of the machine between the final dryer and the winding station or reel-up. Tissue is extremely delicate and difficult to handle, especially at high machine speeds. Generally, improving the tactile qualities of tissue has been achieved by reducing the basis weight and the tensile strength of the web. Lower tensile strength translates into improved softness. Unfortunately, the reductions in basis weight and tensile strength have made it more difficult to achieve high machine speeds because of the difficulty of handling and controlling the weak web in the dry end from the creping doctor to the reel-up.
It would be desirable to provide a method of making a creped tissue paper providing improved tactile qualities while improving the handling and control of the web in the dry end.
The above needs are met and other advantages are achieved by the present invention, which provides a method and apparatus for making a creped tissue that leads to improved tactile qualities of the paper and also facilitates handling and control of the web in the dry end. An apparatus in accordance with the invention comprises a heated drying cylinder on which a tissue paper is dried, a creping doctor for creping the tissue paper from the drying cylinder so as to form a creped tissue paper, at least one carrying fabric spaced downstream of the creping doctor and forming an endless loop about a plurality of guide rolls, a web support extending from proximate the creping doctor to the carrying fabric and supporting and carrying the creped tissue paper thereon, and a reel-up for winding the creped tissue paper onto a building paper roll in the reel-up, the carrying fabric being urged against the building paper roll so as to wind the web thereon.
In some embodiments of the invention, the apparatus includes at least one compression device for compressing the web on the carrying fabric such that the web is substantially reduced in thickness and is improved in surface softness.
A method in accordance with the invention includes steps of creping a tissue paper from a heated drying cylinder, using a web support to guide the web from the creping doctor onto a carrying fabric, carrying the web on the carrying fabric up to the reel-up, and winding the web onto a building paper roll in the reel-up.
In some method embodiments of the invention, there is a further step of transporting the web on the carrying fabric through a compression device where the creped web is compressed to substantially reduce its thickness and improve its surface softness.
In some embodiments of the invention, the carrying fabric and web pass through a compression nip formed between two opposed rolls; optionally, the web can be sandwiched between the carrying fabric and another fabric when it passes through the compression nip. In other embodiments, a first carrying fabric supporting the web forms a nip with a first roll arranged to contact one side of the web to perform a one-sided calendering of the web. The web is then transferred from the first carrying fabric onto a second carrying fabric that forms a nip with a second roll arranged to contact the opposite side of the web to perform calendering on the opposite side of the web.
The compression of the creped web has been found to significantly improve the tactile quality of creped tissue, and in particular gives the tissue a silky feel. By guiding the tissue paper on the web support and then carrying the web on the supporting fabric all the way from the creping doctor to the reel-up, the stability problems associated with open draws are avoided, and the resulting improved web handling ability facilitates high machine speeds.
The compression roll(s) can be room temperature or heated. Preferably, the (or each) carrying fabric is permeable and one or more suction devices (e.g., blow boxes) are arranged within the loop of the/each carrying fabric.
In some embodiments, the web support that guides the web from the creping doctor onto the carrying fabric comprises an air foil. Preferably, the air foil is an active air foil. In other embodiments, the web support comprises another fabric. The other fabric preferably is permeable and a suction device preferably is disposed within the loop of the fabric to ensure that the web adheres to the fabric. The other fabric can pass through the compression nip such that, as previously noted, the web is sandwiched between the two fabrics when it passes through the nip; alternatively, the two fabrics can be arranged in sequence such that the web is transferred from one to another, and each fabric can form a compression nip with a roll as previously noted.
The peripheral speed of the paper roll in the reel-up preferably is greater than the speed of the carrying fabric that carries the web to the reel-up, so that slack in the web is avoided during the reeling.
When a compression roll contacts the web on a carrying fabric, the roll preferably is operated at a peripheral speed less than the speed of the fabric. In this manner, the roll creates slack in the web upstream of the roll and reduces slack in the web downstream of the roll.